1. Field of the Invention
This invention relates to a new process for the production of molded polyurethane articles having densities of about 0.8 to 1.4 g/cm.sup.3 and a flex modulus according to DIN 53,457 of at least about 1800N/mm.sup.2 by the reaction of organic polyisocyanates with compounds containing isocyanate reactive groups in accordance with the reaction injection molding process.
2. Description of the Prior Art
The production of molded articles by the isocyanate polyaddition process is known in principle. Thus, for example, a process for the production of rigid polyurethane molded parts with an internal density gradient distribution is described in DE-PS No. 1,694,138. These molded parts have very good mechanical properties by virtue of their internal structure although their impact strength is not sufficient for all requirements in practice.
Although elastomeric polyurethane molded articles of the kind obtainable, for example, according to DE-OS No. 2,622,951 or DE-OS No. 3,147,736 have high impact strengths, the processes described in these publications are not suitable for the production of molded articles which have a flex modulus according to DIN 53,457 of greater than 1000N/mm.sup.2.
Although molded articles with a very high flex moduli may be obtained according to DE-OS No. 3,405,679, the process disclosed in this publication requires the use of comparatively highly viscous polyester polyols which severely impairs the reliable working up of the polyol mixtures.
The underlying object of the present invention was therefore to provide a new process for the production of molded polyurethane articles by the reaction injection molding process which would not have the disadvantages of the processes known in the art and which would enable molded articles with high impact strengths to be produced with densities of about 0.8 to 1.4 g/cm.sup.3 and flex moduli according to DIN 53,457 of at least about 1800N/mm.sup.2.
This problem has been solved by the process according to the invention described below.